Ethernet Passive Coaxial-cable Network (EPCN) technologies take the Ethernet as a carrier, adopt point-to-multipoint structure and a passive Coaxial-cable transmission mode, and transmit data streaming with a burst Ethernet packet mode in an uplink direction.
FIG. 1 is a schematic diagram illustrating structure of an EPCN system. With reference to FIG. 1, the EPCN system mainly includes a Coaxial-cable Line Terminal (CLT), a brancher/distributor, as well as multiple Coaxial-Cable Network Units (CNUs). The EPCN system connects with various Ethernet devices via the CLT, and connects with user equipment via the CNUs. The EPCN system may be applied to various environments. At present, the most common application of the EPCN system is the Ethernet Broadband connecting to households in a building.
In the EPCN system, the basic process of data transmission is as follows. In the downlink, the CLT transmits data to the brancher/distributor connecting with different users, and the brancher/distributor connecting with different users forwards the data to the CNU of each user. In the uplink, each CNU transmits data to the brancher/distributor connecting with different users according to a certain transmission level, and the brancher/distributor forwards the data to the CLT.
Seen from the data transmission process in the EPCN system, in the uplink, data from any CNU must be transmitted, through the brancher/distributor, to the CLT. Therefore, the brancher/distributor connecting with different users possesses fixed isolation degree, so as to avoid that uplink data which is sent from one CNU to the CLT gets to another CNU through the brancher/distributor. The isolation degree is larger than transmission path loss generated by transmitting the uplink data between the CLT and the brancher/distributor, e.g. 25 dB in general. The brancher/distributor connecting with different users may isolate the uplink data as long as transmission level amplitude for transmitting uplink data by the CNU is less than the isolation degree of the brancher/distributor. That is, the brancher/distributor merely transmits the uplink data to the CLT instead of transmitting the uplink data to CNUs of other users.
However, in practical service applications, the transmission level amplitude adopted by all the CNUs for transmitting uplink data is generally uniform. The uniform transmission level amplitude is determined according to the largest transmission level amplitude required by each CNU. The largest transmission level amplitude is generally larger than the isolation degree of the brancher/distributor connecting with different users, and thus the brancher/distributor connecting with different users cannot isolate the uplink data transmitted by the CNUs, resulting in that the uplink data sent from a CNU of one user is filched by CNUs of other users. Thus, the security of transmitting the uplink data is greatly reduced and the Quality of Service of services is reduced.